Solar simulators based on light‐emitting diodes (LEDs) have shown great promise as alternative light sources for indoor testing of photovoltaic cells with certain characteristics that make them superior to the traditional solar simulators. However, large‐area uniform illumination more suitable for larger cells and module measurements still remain a challenge today. In this paper, we discuss the development and fabrication of a scalable large‐area LED‐based solar simulator that consists of multiple tapered light guides. We demonstrate fine intermixing of many LED light rays and power delivery in the form of a synthesized AM 1.5 spectrum over an area of 25 cm × 50 cm with better than 10% spatial nonuniformity. We present the spectral output, the spatial uniformity, and the temporal stability of the simulator in both the constant current mode and the pulsed‐mode LED operation, and compare our data with the International Electrotechnical Commission standards on solar simulators for class rating. Although the light intensity with our current design and settings falls short of the standard solar AM 1.5 intensity, this design and further improvements open up the possibility of achieving large‐area, high‐power indoor solar simulation with various desired spectra. Copyright © 2011 John Wiley & Sons, Ltd.

Active interrogation is a method used to enhance the likelihood of detection of shielded special nuclear material (SNM); an external source of radiation is used to interrogate a target and to stimulate fission within any SNM present. Radiation produced by the fission process can be detected and used to infer the presence of the SNM. The Atomic Weapons Establishment (AWE) and the Naval Research Laboratory (NRL) have carried out a joint experimental study into the use of single pulse, high-intensity sources of bremsstrahlung x-rays and photoneutrons in an active interrogation system. The source was operated in both x-ray-only and mixed x-ray/photoneutron modes, and was used to irradiate a depleted uranium (DU) target which was enclosed by up to of steel shielding. Resulting radiation signatures were measured by a suite of over 80 detectors and the data used to characterise detectable fission signatures as a function of the areal mass of the shielding. This paper describes the work carried out and discusses data collected with proportional counters, NaI(Tl) scintillators and Eljen EJ-309 liquid scintillators. Results with the x-ray-only source demonstrate detection ( ) of the DU target through a minimum of of steel, dropping to when using a mixed x-ray/photoneutron source. The proportional counters demonstrate detection ( ) of the DU target through the maximum steel shielding deployed for both photon and mixed x-ray/photoneutron sources.Index Terms-Active interrogation, bremsstrahlung x-ray, electron accelerators, nuclear security, photoneutron, special nuclear material (SNM).

The superconducting radio frequency (SRF) part of the Accelerator Production of Tritium (APT) linac will accelerate a 100-mA proton beam from 217 MeV to 1700 MeV. Since SRF cavities can accept protons over a wide velocity range, cavities with only two different betas are required; however, three different length cryomodules are required. A modular design was adopted that will reduce the engineering and design effort to produce these cryomodules. A final design of the APT Engineering Development and Demonstration (ED&D) cryomodule for a two-cavity β=0.64 cryomodule has been completed, and a single cryomodule will be fabricated by industry next year. The cavities will be cooled in a 2.15-K superfluid helium bath similar to the Continuous Electron Beam Accelerator (CEBAF) system. What sets the APT cryomodules apart is the high radio frequency (RF) power that must be delivered to the cavities. The RF losses in the cavities and power couplers place a large heat load on the central helium liquifier. Minimizing these loads required extensive iterations of the power coupler cooling schemes and thermal shield. A spoke support arrangement was developed to keep the beam centerline fixed and to minimize forces acting on the helium vessel/cavity during cool down. Laminar flow through the cryomodule during clean room assembly dictated the use of a vacuum vessel with large top and bottom openings. Analyses were performed to ensure structural integrity under vacuum loading, while also minimizing vessel deflections which could impact beam centerline positioning.The structural/thermal analysis used to optimize the cryomodule design will be presented in this paper.

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The design for the superconducting cavities of the highenergy accelerator for the Accelerator Production of Tritium (APT) project has been extensively changed in the last two years. The original accelerator design incorporated 0.48 and 0.71 beta cavities with stiffeners, and a stainless-steel helium vessel. Today, the accelerator uses unstiffened 0.64 and 0.82 beta cavities, and a titanium helium vessel. This paper discusses the design process, including the supporting analyses, prototype cavities built, and the decisions made to support the current design. The design of the integrated cavity-helium vessel is presented. Future plans and testing for design validation are also discussed.